At present, in white LED, the mainstream is a method where a composite for wavelength conversion composed of a resin and a phosphor is provided on a light emitting element and a blue light emitted from the light emitting element and a yellow light obtained by wavelength conversion of a part of the blue light through applying the blue light to the phosphor are mixed in the composite to obtain a white light.
However, the resin constituting the composite tends to deteriorate gradually by light or heat generated from the light emitting element and thus there is a problem that properties such as durability, heat resistance, and emission intensity decrease.
Therefore, there have been performed studies each using a ceramics composite consisting of an inorganic material with no resin as a composite for wavelength conversion.
For example, Patent Document 1 discloses a massive phosphor consisting of an inorganic material and having a surface roughness (Ra) of 0.05 to 3 μm, in which the inorganic material is composed of crystallized glass, and the crystallized glass is obtained by precipitating YAG crystals or a YAG crystal solid solution containing Ce3+.
Moreover, Patent Document 2 discloses a phosphor having a polycrystalline ceramics structure including a phosphor of doped YAG type, in which the phosphor is embedded in a ceramics matrix containing non-luminescent polycrystalline alumina, the ceramics matrix includes 80 to 99.99 vol. % of alumina and 0.01 to 20 vol. % of the phosphor, and the phosphor has the composition (Lu1-x-y-a-bYxGdy)3(Al1-zGaz)5O12:CeaPrb where 0<x≦1; 0≦y<1; 0≦z≦0.1; 0≦a≦0.2 and 0≦b≦0.1, and a+b>0.
Patent Document 1: JP-A-2007-161944
Patent Document 2: JP-T-2008-533270